Composition for and method of forming oxalate coatings on ferrous metal surfaces



United States Patent 2,791,525 COIVIPOSITION FOR AND METHOD OF FORMINGOXALATE COATINGS 0N FERROUS METAL SURFACES Werner Rausch, Frankfurt amMain, and Arthur Mayr, Frankfurt am Main Sossenheim, Germany, assignorsto Parker Rust Proof Company, Detroit, Mich, a corporation of MichiganNo Drawing. Application November 6, 1953, Serial No. 390,734

Claims priority, application Germany November 11, 1952 12 Claims. (Cl.148-6.14)

The present invention relates to compositions for and a method ofproducing firm, adherent oxalate coatings on ferrous metals which serveas an excellent surface protector during metal deformation operationsand which are also suitable as a base for paint.

Various processes for the formation of ferrous oxalate coatings on ironand steel surfaces have been known and used for many years. Boilingoxalic acid was early proposed for this purpose and improved uponsomewhat later by the employment of oxidizing agents, such as sulfitesand peroxides. A number of other special additives have been proposed toincrease the rate of reactivity of aqueous oxalic acid solutions onmetals which are difficult to coat, such as stainless steel, includingthe ferric ion, and the halides. It has also been proposed to formoxalate coatings on iron, steel and stainless steel by the use ofaqueous solutions containing oxalic acid, alkali metal phosphate and achromate.

Most of the heretofore known ferrous oxalate coatings have beenrelatively soft and contain a large proportion of dust as an outerlayer. Soft dusty coatings are useful and serve as an effective partinglayer between the die and the metal in metal deformation operations.However, such soft, dusty oxalate coatings are insufficiently adherentto be effective in all types of metal deformation, being of least valuewhere the deformation is extreme. While the inclusion in aqueous oxalicacid solutions of alkali metal phosphates and chromates improves the adherence of the resultant coating, the most adherent coatings are formedonly as the pH value of the operating solution is allowed to increasetoward about 3.0. At such pH values the operating solutions have atendency to produce undesirable quantities of sludge.

It is the primary object of the present invention to provide acomposition which will produce on a metallic sur' face contactedtherewith a firmly adherent oxalate coating while producing practicallyno sludge in the operating solution.

Another important object is to provide a method for forming firmadherent oxalate coatings on ferrous surfaces which are relatively freeof dust and especially suitable for use in deformation operations, or asa base for paint, Varnish, lacquer, enamel or other conventional finishcoating.

A further objective of this invention is to provide a method for formingoxalate coatings on ferrous surfaces which is easily controlled,inexpensive to operate and which produces a minimum of undesirablesludge.

A still further object is to provide a replenishing material suitablefor maintaining such compositions at proper strength during continuousprocessing.

Other objects and advantageous features of this inven tion will becomeapparent upon considering the present disclosure in its entirety.

In accordance with the present invention, the above and related objectsare achieved by the use in aqueous oxalic acid solutions of thefluoborate ion in conjunction with a suitable oxidizing agent.Optionally the compositions ice of this invention may include thealuminum ion. The presence of the aluminum ion has been found to producecoatings on ferrous surfaces having higher adherence than is obtainablein its absence, and the preferred compositions of this invention includethe aluminum ion.

The fluoborate ion may be introduced into an aqueous oxalic acidsolution in various forms such as fiuoboric acid or the alkali metalsalts thereof, for example, the sodium or potassium fluoborates, thesalt form being preferred.

Oxidizing agents which are capable of oxidizing the ferrous ion to theferric ion in an aqueous oxalic acid solution Without concurrentlyoxidizing the oxalic acid may be satisfactorily used for the purposes ofthis invention. Suitable oxidizing agents include the chlorates,bromates, iodates, nitrites and hydrogen peroxide. Unusually strongoxidizing agents such as permanganate and nitrate are not recommendedfor use because of their tendency to rapidly oxidize the oxalic acid.Similarly, the relatively Weak oxidizing agents such as the organicnitro compounds including sodium meta nitro benzene sulfonate, picricacid, etc. are not nearly as desirable as chlorates, 'brornates,nitrites and peroxide'although some limited benefit may be obtained fromtheir use.

The presence of both the fluoborate ion and a suitable oxidizing agentin the aqueous oxalic acid solutions of this invention enables theoperation of the solutions at pH values well below that usually employedwhen phosphoric acid is present as an ingredient in such solutions, andfor best results it is advisable to maintain the pH of the operatingsolution in the range of 0.7 to 2.0 and preferably in the range of 1.0to 1.3. Under such conditions the resultant coating is firm, adherentand relatively free of dust, and even after extended continuousoperation there is only an extremely minor amount of sludge formed inthe operating solution. 1

Broadly, the proportion of the ingredients which are suitable for use inthe aqueous compositions of this invention are set forth in Table I.

TABLE I Concentration grams/liter Fluoborate ion (BFr) 1.6-12.0 Chlorateion (C10?) ODS-2.0 Oxalic acid 5-15 The other oxidizing agents indicatedabove to be suitable for use may be employed in suitable quantities toproduce equivalent oxidizing of the ferrous to ferric ion in thesolution. For the bromates and iodates approximately the same quantityis required as that indicated for chlorates, while somewhat smallernumerical quantities of nitrites and peroxide are satisfactory.

For the production of oxalate coatings on ferrous surfaces with thesolutions of the type set forth in Table I having the highest order ofadherence it is desirable to incorporate in such solutions a proportionof the aluminum ion between about 0.3 gram/liter and about 1.6grams/liter. The aluminum ion may be introduced in the form of analuminum salt such as aluminum sulfate or aluminum oxalate. Care shouldbe taken however, in introducing aluminum not to concurrently introducean undesirable anion such as nitrates or chlorides. The presence ofchloride has been found to be undesirable, and nitrates are incompatiblewith the oxalic acid.

In general the method of this invention comprises the steps ofcontacting a preliminarily cleaned metallic surface with thecompositions of this invention at a suitable temperature and for asuitable time, separating the part from the solution, rinsing and dryingthe coating. Thereafter, and if desired, the coating may be either oiledin a conventional manner to further enhance the corrosion resistance orit may be painted, varnished, lacquered, enameled or coated with othersiccative finishcoating. Additionally, the coating may be treated withlime or other lubricants conventionally employed for such purpose, suchas soaps, and the coated part thereafter subjectcd to deformation. Evenwithout subsequent treatment after rinsing, the coatings of thisinvention have proved to be very effective in the deep extrusion ofsheet iron, pipes, tubes and wires. The temperature of the solution andtime of contact are not critical, and a wide variety of conditions maybe satisfactorily used. Temperatures between about 90 F. and 160 F. andtimes between about 3 and 15 minutes may be employed. One of theadvantageous features of this invention is that relatively lowtemperatures such as 105 F. to 120 F. produce more adherent coatingsthan higher temperatures. Preferred operating conditions are attemperatures of 105 F.-l20 F. for to minutes.

The compositions and method of this invention are illustrated in greaterdetail in the following examples.

Example 1 A 1 liter solution was prepared containing 5 grams sodiumfluoborate, 5 grams aluminum sulfate -18H2O, 10 grams oxalic acid -H2O,2 grams sodium chlorate. Low carbon steel panels having a surface areaof 128 square inches, preliminarily degreased and pickled in coldhydrochloric acid were inserted in the solution at 113 F. for 5 minutesand withdrawn. The pH of the solution was between 1.0 and 1.2. 50 suchpanels were inserted in this solution and all of the panels uponwithdrawal were found to be coated with a firm, adherent, greenishgraycolored coating. A check on the surface weight of the coatings showed anaverage of 418 mg./sq. ft. Periodic checking during the processing tomaintain the concentration of the ingredients at the initial levelsrequired the addition of 16.6 grams of oxalic acid -2Hz0 and 6 grams ofsodium chlorate.

A more complete check on the depletion of the ingredients showed thatthe ingredients were depleted at the following rates:

Oxalic acid -2Hz0 1 lb./1000 sq. ft. Sodium chlorate .4 lb./ 1000 sq.ft. Aluminum sulfate -18H2O .15 lb./1000 sq. ft. Sodium fluoborate .16lb./ 1000 sq. ft.

A concentrated replenishing material which was found to be suitable formaintaining the ingredients within the above prescribed ranges ofproportions was prepared having the following composition by weight:6667% oxalic acid -2H2O, 17% sodium fluoborate, 15-17% aluminum sulfate-18H2O. This concentrate may be added periodically as necessary.

Example 2 A 200 liter bath was compounded and analyzed to contain thefollowing: 5 grams/liter sodium fluoborate, 10 grams/liter oxalic acid-2H2O, 5 grams/liter aluminum sulfate 181-120, and 2 grams/liter sodiumchlorate. The bath was maintained at about 110 F. and was used forimmersing steel wires having a Mohs scale hardness of about 5 and adiameter of about .08 inch. The wires were preliminarily pickled in coldhydrochloric acid and water rinsed before immersion in the heatedoxalate solution for about 10 minutes. The wire was withdrawn, coldwater rinsed, dipped in a dilute lime suspension and dried at 110 C. Thecoated wire was then drawn on multiple extrusion machines in a series of8 drawings to reduce the diameter to .031 inch, a total decrease of 84%,at a velocity of 315 feet per minute. The surface of the wire wasinspected after drawing and found to be uniformly smooth. After drawing1100 pounds of wire, very little wear could be detected on the Surfaceof the extrusion dies.

1 Example 3 An oxalate solution was prepared having the composition ofthat set forth in Example 2 and 10 steel tubes 2.6 feet long wereimmersed in the solution at 113 F. for 10 minutes and withdrawn. Thesurface of the tubes was covered with a firmly adherent, dark oxalatecoating. After drying, the tubes were treated with dry soap and two ofthe tubes were drawn dry and two of the tubes were drawn wet in 4 passesto obtain a decrease in crosssection of 72%. The surfaces of all tubesafter drawing were uniformly smooth and free from slivers or breaks.

What is claimed is:

l. A composition for forming oxalate coatings on metallic surfaces whichcomprises an aqueous solution consisting essentially of about 1.6 toabout 12 grams per liter of the fluoborate ion, about 0.08 to about 2.0grams/liter of the chlorate ion and about 5 to'about 15 grams/liter ofoxalic acid, said composition having a pH in the range of 0.7 to 2.0.

2. A composition of matter which comprises an aqueous solutionconsisting essentially of about 1.6 to about 12 grams/liter of thefluoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion,about 0.3 to about 1.6 grams/ liter of the aluminum ion and about 5 toabout 15 grams/liter of oxalic acid, said composition having a pH. inthe range of 0.7 to 2.0.

3. A replenishing material for replenishing an aqueous solutioncomprising oxalic acid, the fluoborate ion and the aluminum ion whichmaterial consists of in percentage by weight: 66%-67% oxalic aciddihydrate, 15% 17% sodium fluoborate, 15 %17% aluminum sulfate 131-120.

4. A method for forming an oxalate coating on metallic surfaces whichcomprises the steps of contacting the metal surface to be coated with anaqueous composition consisting essentially of about 1.6 to about 12grams/liter of the fluoborate ion, about 0.08-about 2.0 grams/liter ofthe chlorate ion and about 5 to about 15 grams/liter of oxalic acid,said composition having a pH in the range of 0.7 to 2.0.

5. A method for forming an oxalate coating on metallic surfaces whichcomprises the steps of contacting the metal surface to be coated with anaqueous composition consisting essentially of about 1.6 to about 12grams/liter of the fluoborate ion, about 0.08 to about 2.0 grams/literof the chlorate ion, about 0.3 to about 1.6 grams/liter of aluminum ionand about 5 to about 15 grams/liter of oxalic acid, said compositionhaving a pH in the range of 0.7 to 2.0.

6. A method for deforming metal which comprises the steps of contactingthe metal surface to be drawn with an aqueous composition consistingessentially of about 1.6 to about 12 grams/liter of the fluoborate ion,about 0.08 to about 2.0 grams/ liter of the chlorate ion and about 5 toabout 15 grams/liter of oxalic acid, said composition having a pH in therange of 0.7 to 2.0, drying the coating grams/liter to about 12grams/liter of the fluoborate ion,

about 0.08 to about 2.0 grams/ liter of the chlorate ion and about 5 toabout 15 grams/liter of oxalic acid, said composition having a pH in therange of0.7 to 2.0, treating the coating with a lubricant, drying thecoating on the metal surface and thereafter deforming the coated metal.

8. A method for deforming metal which comprises the steps of contactingthe metal surface to be drawn with an aqueous composition consistingessentially of about 1.6 to about 12 grams/liter of the fluoborate ion,about 0.08 to about 2.0 grams/liter of the chlorate ion, about 5 toabout 15 grams/liter of oxalic acid and about 0.6 to about 1,6grams/liter of the aluminum ion, said composition having a pH in therange of 0.7 to 2.0, drying the coating on the metal surface andthereafter subjecting the coated metal to deformation.

9. A method for finishing metallic surfaces which comprises the steps ofcontacting the metal surface to be finished with an aqueous solutionconsisting essentially of about 1.6 to about 12 grams/liter offiuoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion,and about grams/liter to about 15 grams/liter of oxalic acid, saidcomposition having a pH in the range of 0.7 to 2.0, and thereaftercovering the coated metal with a siccative coating.

10. A method for finishing metallic surfaces which comprises the stepsof contacting the metal surface to be finished with an aqueous solutionconsisting essentially of about 1.6 to about 12 grams/liter offiuoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion,and about 5 grams/liter to about 15 grams/liter of oxalic acid and about0.3 to about 1.6 grams/liter of the aluminum ion, said compositionhaving a pH in the range of 0.7 to 2.0, and thereafter covering thecoated metal with a siccative coating.

11. A composition of matter which comprises an aqueous solutionconsisting essentially of about 1.6 to about 12 grams/liter of thefluoborate ion, about 5 to about 15 grams/ liter of oxalic acid and atleast one oxidizing agent selected from the group consisting ofchlorates,

bromates, iodates, nitrites and hydrogen peroxide in an amountsuflicient to produce an equivalent oxidizing efiect as that produced byabout 0.08 to about 2.0 grams/liter of the chlorate ion, saidcomposition having a pH in the range of 0.7 to 2.0.

12. A method for forming an oxalate coating on metallic surfaces whichcomprises the steps of contacting the metal surface to be coated with anaqueous composition consisting essentially of about 1.6 to about 12grams/ liter of the fluoborate ion, about 5 to about 15 grams/ liter ofoxalic acid and at least one oxidizing agent selected from the groupconsisting of chlorates, bromates, iodates, nitrites and hydrogenperoxide in an amount sufi'icient to produce an equivalent oxidizingeffect as that produced by about 0.08 to about 2.0 grams/liter of thechlorate ion, said composition having a pH in the range of 0.7 to 2.0.

References Cited in the file of this patent UNITED STATES PATENTS2,066,842 Lodeesen Jan. 5, 1937 2,081,449 Cook May 25, 1937 2,273,234Tanner Feb. 17, 1942 2,500,673 Gibson et al. Mar. 14, 1950 2,669,532Gibson Feb. 16, 1954 2,672,976 Overath et al. Mar. 23, 1954

1. A COMPOSITION FOR FORMING OXALATE COATINGS ON METALLIC SURFACES WHICHCOMPRISES AN AQUEOUS SOLUTION CONSISTING ESSETIALLY OF ABOUT 1.6 TOABOUT 12 GRAMS PER LITER OF THE FLUOBORATE ION, ABOUT 0.08 TO ABOUT 2.0GRAMS/LITER OF THE CHLORATE ION AND ABOUT 5 TO ABOUT 15 GRAMS/LITER OFOXALIC ACID, SAID COMPOSITION HAVING A PH IN THE RANGE OF 0.7 TO 2.0.